The present invention relates to a method of disposing of particulates, in particular carbon, removed from the exhaust gases of an internal combustion engine, especially a Diesel engine, where the exhaust gases are passed through the filter means of a particulate filter to separate-off the particulates, and the particulates retained are caused to burn with the aid of an electrical current source during operation of the engine. The invention also relates to apparatus for implementing such a method.
In addition to the presence of oxygen (in the case of Diesel engines, there is sufficient oxygen contained in the exhaust gas because such engines are operated with excess oxygen), the combustion of carbon particles to form carbon dioxide calls for temperatures such as do not generally exist in the exhaust gases at no load (idling) or part load. In order to effect ignition of the carbon particles despite this, it is known to add external energy in order to achieve the necessary ignition temperature level.
For instance, it is proposed in German Offenlegungsschrift No. 25 19 609 Hafner et al dated Nov. 11, 1976, and in German Offenlegungsschrift No. 27 56 570 -Crone dated Sept. 28, 1978, to provide ignition sources (electrically-heated glow plugs or heating coils) upstream of the filter. Since the exhaust gas heated in this manner will transmit heat not only to the particulate deposits in the filter but, in an undesirable manner, also to the filter material and all pipe walls existing downstreamnot to speak of the storage heat requirements of the electric heating elements -, it will be readily appreciated that the electrical auxiliary energy is used very uneconomically.
Improved utilization of the auxiliary energy is made in German Pat. No. 30 24 539 Erdmannsdorfer et al dated June 9, 1982. Here, the particulates separated-off in a non-metallic depth filter are heated as required up to the ignition temperature by the electromagnetic radiation of a microwave generator that is coupled in circuit via a wave guide. The cost involved for the microwave generator is, however, not inconsiderable.
The object of the present invention is to provide equally good auxiliary energy utilization as in German Pat. No. 30 24 539 Erdmannsdorfer et al dated June 9, 1982 using simple apparatus of relatively low cost and complexity. Furthermore, reliable and unproblematic burn-off of the particular deposits on the filter is to be achieved without affecting the filter itself or parts of the electric ignition energy supply. In this concept, the auxiliary energy is intended to be converted almost exclusively in the carbon particles retained in the filter, i.e. only the particulates themselves are heated and caused to burn through the internal heat thus produced. The residual oxygen in the exhaust gas consequently finds an already preheated carbon particle surface with which it can immediately react exothermically.